In construction machinery in which a plurality of work machines (for example, an arm, a bucket, a boom, a turret device, and a travel device of a hydraulic shovel) and auxiliary machines (for example, an engine cooling fan) are driven by the oil supplied under pressure from a plurality of hydraulic pumps driven by an engine, the process of setting the engine output characteristic (revolution speed and output torque) according to a selected work mode, controlling the total absorption torque (a product of discharge quantities of oil per one revolution and oil pressures)of the plural hydraulic pumps so as to obtain the predetermined characteristic, and controlling the operation point of the engine to a matching point of the output torque of the engine and the absorption torque of the hydraulic pumps is known (see, for example, Japanese Patent Application Laid-open No. 2-38630, Pages 2-9, FIGS. 1-7, FIGS. 18-21).
FIGS. 11(a) and (b) are engine output characteristic diagrams illustrating the control performed in various work modes described in Japanese Patent Application Laid-open No. 2-38630. According to Japanese Patent Application Laid-open No. 2-38630, for example, when a heavy excavation mode is selected as a work mode in a hydraulic shovel, then the position of the governor level of the engine is controlled so that the maximum target engine revolution speed (referred to hereinbelow as a high-idle revolution speed) becomes the maximum revolution speed N′A, as shown in FIG. 11(a), and the highest-speed regulation line LA is thereby set. Furthermore, a plurality of hydraulic pumps are controlled so as to absorb the torque on an equal horsepower characteristic AH passing through a maximum horsepower point PH on the highest-speed regulation line LA, and a total absorption torque thereof is controlled following the characteristic A′H shown the figure. The output torque of the engine and the absorption torque of the hydraulic pumps are thus matched at a horsepower point PH. Furthermore, for example, when a light excavation mode (economy mode) is selected, then a lower speed regulation line LB is set by setting the high-idle revolution speed to a lower revolution speed N′B, as shown in FIG. 11(b), and the total absorption torque of the hydraulic pumps is controlled along a smaller equal horsepower characteristic AS. As a result, the output torque of the engine and the absorption torque of the hydraulic pumps will be matched at the horsepower point P′S on the low-speed regulation line LB and the engine will operate at the revolution speed NB. In the heavy excavation mode, because a large horsepower can be outputted from the engine, the work can be performed efficiently. On the other hand, in the light excavation mode, because the output horsepower from the engine is decreased, fuel consumption is reduced.